Gas turbine engines are used for a variety of purposes including electric utility and industrial powerplant applications. Governmental regulations have been implemented which limit powerplant emissions of particles such as nitrous oxide (NOx) and carbon monoxide (CO). In efforts to reduce NOx emissions, powerplants have incorporated engines which inject steam or water into the engine's combustor. Injecting steam into the combustor reduces the temperature to which air is heated by the combustion of fuel. NOx emissions are significantly reduced by steam injection since NOx emissions decrease as flame temperatures decrease. Unfortunately, as the lowest NOx levels are obtained it has been found that carbon monoxide emissions significantly increase.
One powerplant system for obtaining low NOx and CO emissions is selective catalytic reduction (SCR). However, this system requires significant capital and operating expenses and this system also unfortunately involves the commercial transportation of ammonia which is both hazardous and relatively expensive.
Reformers or chemical recuperators transform fuels such as natural gas into high hydrogen content streams for use in producing ammonia or for use in refinery processes requiring hydrogen. These reformers may incorporate heating systems which use fire-brick which heat the reformer by convection and radiation. However, these fire-brick systems are typically expensive and operate at much higher temperatures than desired for incorporation with gas turbines.
The combining of gas turbine engine technology, and in particular aircraft derivative engines, with reformers has typically been considered impractical based on cost, efficiency and design considerations. In one suggested advanced powerplant, described as a reheat intercooled steam injected gas turbine engine, low and high pressure compressors in a gas turbine engine produce a downstream fluid flow and an intercooler is positioned between the compressors. The fluid flow passes through a combustor which heats the fluid and then the fluid flow passes through high and low pressure turbines which drive the compressors. A reheat combustor is positioned downstream of the low pressure turbine for further heating of the fluid flow. The flow then passes through a power turbine and the output flow from the power turbine provides heat for a reformer. The reformer receives water which is heated by the intercooler and the reformer also receives methane which is heated by a fuel heater which uses the intercooler's heated water. The reformer produces a reformed fuel which is supplied to both the first combustor and the reheat combustor. Steam from a boiler is also injected into the turbine for cooling. While this system may be capable of producing low NOx and CO emissions, this system is unfortunately complex. For example, the exhaust from the power turbine which heats the reformer typically must be at least about 1150 to 1250 degrees Fahrenheit and generally must be about 1200 to 1800 degrees Fahrenheit. However, the exhaust from a gas turbine engine is typically only about 900 degrees Fahrenheit. Therefore, the reheat combustor must produce a fluid flow whose temperature is in excess of these temperatures and the power turbine must be designed to withstand these types of temperatures. However, reheat combustors have not generally been incorporated in gas turbine configurations and therefore design, development and their associated expenses are required in reheat combustor development. Further, power turbines are generally not currently capable of withstanding these temperatures and thus redesign and replacement is necessary with turbines incorporating advanced cooling techniques, therefore resulting in increased expense. Further, the intercooler and fuel heater which provide heated inputs into the reformer also result in increased design complexity and expense and provide increased difficulties in modifying existing systems.
Therefore, it would be desirable to have a gas turbine powerplant with reduce NOx and CO emissions which is capable of producing and utilizing reformed fuel and which may be adapted to current systems without significant design modifications and expense which preferably eliminates the use of extremely high temperature power turbines.